Longitudinal data on the composition of salivary microorganisms in type 1 diabetes mellitus (T1DM) patients are lacking. This study aimed to characterize and compare the salivary microbiota of children with and without T1DM in a longitudinal approach. We hypothesized that the bacterial composition in saliva differs between healthy and T1DM children in a 1-year period.

Overall, 55 children (4–15 years old; 26 with T1DM, 29 healthy controls) completed the study. Oral examinations (plaque index, bleeding on probing, and Decayed, Missing, Filled Teeth index) and unstimulated saliva sampling were performed at baseline and after 1 year. Microbial composition was assessed via 16S rRNA gene sequencing (V1-V3 region) and referenced against the Human Oral Microbiome Database.

Beta diversity analysis (Principal coordinate analysis (PCoA)) showed greater separation between groups at baseline than at follow-up. Linear discriminant analysis effect size identified that T1DM was associated with Fusobacterium species, whereas Rothia species associated with health. Alpha diversity indexes (Chao 1, Shannon and Simpson) showed no significant differences between the groups (P>0.05).

Our results demonstrated that the salivary microbiota of T1DM children is significantly distinct from healthy controls during 1-year of follow-up. Future studies are needed to reveal whether improved T1DM management benefits microbial composition.

The microbial shift in diabetic children may contribute to increased susceptibility to oral diseases, highlighting the importance of preventive dental care in this population.